Anisotropic visible and infrared(IR).absorption spectra of Langmuir-Blodgett(LB).films of mutually mixed merocyanine dyes deposited with Cd2+ ions were recorded. In these films, a merocyanine dye ‘DO’ is included in J-aggregates, although in LB films of DO(not mixed with other merocyanine dyes), DO itself does not form J-aggregates. A difference spectrum method successfully separated the spectra observed into two components, one of which was due to J-aggregates. This component includes the contribution of the J-aggregated DO molecules and compared well with the absorption spectra observed for LB films of DO. This comparison detected, for the aggregated DO, red shifts of several IR bands due to softening of the bond alternation in the central conjugated system of the molecule, which thus suggested that intramolecular charge transfer is enhanced by the formation of J-aggregates.

J-aggregates in Langmuir
Blodgett (LB). films of mutually mixed merocyanine dyes were characterized by using Fourier transform infrared(FT-IR).spectroscopy. Two merocyanine dyes, one which forms and one which does not form J-aggregates in their LB films with fatty acids and divalent metals, so-called 6MeDS and DO, respectively, were used in this study. In LB films of DO-6MeDS mutual mixtures, most DO molecules are included in J-aggregates. The IR spectra of these films were measured and compared with linear combinations of the spectra for DO and 6MeDS films. The difference between the measured and the calculated IR spectra reflects the difference between the electronic state of J-aggregated DO and that of monomeric DO. The results suggest an enhancement of the intramolecular charge transfer induced by the formation of J-aggregates.

Langmuir-Blodgett films of mixtures of fatty acids (FA) and a merocyanine dye (DS), bearing one long alkyl chain and one carboxylic group, were prepared at a nitrogen-pure water interface. The films exhibit a distinct and highly anisotropic J-band near 605 nm, even though they do not contain any metallic or ammonium cations. Although an isotropic band was seen in the region of 500-550 nm, the contribution of the J-aggregates was extracted from the observed visible and IR absorption spectra by using the difference in the polarization of the bands. This analysis indicates a change in the electronic structure of DS in the J-aggregates, probably corresponding to intramolecular charge transfer. Furthermore, this analysis also suggests that in this metalfree case, the formation of the J-aggregates is strongly affected by the hydrogen bonding between the carboxylic groups in two DS and that between the carboxylic groups in DS and FA.

Langmuir–Blodgett (LB) films of mixtures of 3,4,9,10-perylenetetracarboxylic diimide (PTCDI), merocyanine dye (DO) and arachidic acid(C20) with different molecular ratios, were prepared on Cd2+-containing and pure-water subphases. The characterization of mixed Langmuir and LB films were performed by using, respectively, surface pressure-molecular area isothermetry and UV-Vis-IR absorption spectroscopy. The analysis indicates that interaction between the two dyes modifies their arrangements and electronic states in their mixed Langmuir films spread upon the Cd2+-containing subphase. However, the mixed LB films with the pure-water subphase are showed to be simple physical mixtures. The difference in the mixing effect observed for the Langmuir films upon the Cd-containing and pure-water subphases may be caused by the formation of metal chelation with the former subphase.

LB films of organic-inorganic charge-transfer systems, Cu-complexes of 2-methyl-5-octadecyIDCNQI(C18MeDCNQI) and 2-alkylTCNQ(CnTCNQ with n=12,15 and 18), were successfully fabricated by utillizing the airwater interface as a reaction field for the reduction of the acceptor moieties. The charge transfer degrees of the C18MeDCNQI and CnTCNQ in the LB films were estimated at -1, respectively, from the changes in their IR absorption spectra upon the reduction. The molecular orientation in the films were discussed on the basis of polarized IR spectroscopy. It is suggested that the molecular orientation in the present LB films is largely affected by the coordinate bonds between the Cu cations and the cyanic groups.